In data communication or linear applications, it is crucial to develop circuits with high bandwidth and low jitter. Additionally, having an amplifier with variable gain allows for circuit topologies which can handle large input dynamic ranges without performance degradation. To this end, fully differential circuits are well known for realizing low jitter circuits due to their inherent common-mode rejection and supply rejection characteristics.
Standard five transistor transconductor circuits have been used as differential to single ended converters (current mode logic (CML) to CMOS converters), but due to their inherent imbalances the jitter performance suffers since the current source will usually be pulled in and out of saturation. These transconductors are very simple, well understood, small, and low-power though, so it is preferable to try and use these circuits.